It is well known to employ glass beads containing alkali metals as sources in thermionic gas chromatographic detectors. Detectors utilizing such beads are particularly useful as nitrogen and phosphorous detectors. Such a detector is disclosed in U.S. Pat. No. 3,852,037 of Kolb et al. which issued Dec. 3, 1974. Methods of manufacturing such beads are disclosed, inter alia, in an article by Greenhalgh, Muller, and Aue in 16 Journal of Chromatographic Science 8 of January 1978 and in an article by Lubkowitz, Semonian, Galobardes, and Rogers appearing in 50 Analytical Chemistry No. 4, 672, April 1978.
Particularly advantageous beads include rubidium or cesium-containing glass. Currently, such beads are produced heating the ends of two soda-lime glass rods to a molten state by means of a hydrogen-hydrocarbon torch flame. The molten rod ends are dipped into a rubidium powder. The rod ends are then remelted and touched together. The resultant rubidium-glass mixture is then pulled into fine fibers in the flame. Using the same flame, small pieces of these rubidium-glass fibers are then melted onto a platinum wire until, by trial and error, a bead of 1 mm (.+-.0.1 mm) diameter is obtained. Frequently during heating the platinum wire is overheated, droops, and is then straightened by pulling from both ends.
The rubidium-containing beads produced in this manner are subject to a high rejection rate. They are expensive, neither physically nor chemically uniform, and are short lived. Due to having been stressed during manufacture, the beads may have air voids and fractures and the platinum wire frequently breaks in use.
Accordingly, it is a primary object of the present invention to provide an improved method of manufacturing such beads. Another object is to provide such a method wherein the beads are more uniform, contain a preselected and known volume of material, and are more reproducible. Other objects, features and advantage will be apparent from the following description and appended claims.